1. Field of the Invention
The present invention relates to a mounting assembly used in a railroad car truck and adapted to be positioned between a side frame pedestal and the roller bearing, and more specifically, to such a mounting assembly having a relatively low profile or thickness.
2. Description of Related Art
Mounting assemblies including a shear pad and mating roller bearing adapter have long been known in railroad car trucks for supporting the truck side frames on the wheelsets. Initially, such mounting assemblies included shear pads using metal wear surfaces which permitted limited lateral and longitudinal movement of the side frames relative to the roller bearing adapters positioned on the wheelsets. Subsequently, elastomeric mountings took the place of the metal wear surfaces to provide controlled flexibility in all directions, particularly for self-steering rail car trucks.
U.S. Pat. No. 5,237,933, which is hereby incorporated herein by reference, improved the elastomeric mounting by the addition of a single metal shim sandwiched between two elastomeric layers. While the shear pad described in the '933 patent and similar shear pads with multiple metal plate and rubber layers tend to have improved service life, a common problem is that they have a thickness of approximately one inch. In contrast, older shear pad assemblies tended to have a thickness in the range of approximately 1.06 inches. This relatively large thickness, if not compensated for elsewhere, will increase the ride height of the car. If one car is equipped with the thicker elastomeric shear pad and an adjacent car is not, the couplers will have different heights, thereby preventing a secure fit between the one car's coupler and the coupler of the adjacent car.
In response to this concern, special side frames having a reduced thickness or profile are used in combination with such thicker mounting assemblies. While this is practicable for a new truck, an existing truck having standard side frames cannot be retrofitted with these thicker shear pads. This is especially problematic in view of recently heightened performance requirements from the American Association of Railroads, such as those outlined in AAR M-976. The thinner shear pads that provide a proper ride height with standard mounting assemblies and side frames typically may not conform to the new performance standards, while thicker mounting assemblies that do conform to the new performance standards provide an improper ride height when coupled with cars having standard trucks.
Accordingly, a general aspect or object of the present invention is to provide a mounting assembly suitable for retrofitting to standard side frames.
Another aspect and object of the present invention is to provide a retrofittable mounting assembly that conforms to current performance standards.
Other aspects, objects and advantages of the present invention, including the various features used in various combinations, will be understood from the following description according to preferred embodiments of the present invention, taken in conjunction with the drawings in which certain specific features are shown.